The present invention relates to a method for reducing knocking in an internal combustion engine in which knocking of the engine is detected to control at least one of a plurality of parameters determining the operational characteristics of the engine.
It has been known that the occurrence of knocking depends upon various .factors determining the engine performance, such as the ignition timing, air-to-fuel ratio, intake air temperature, intake air humidity, combustion chamber temperature, etc. Among these, the ignition timing and the air-fuel ratio are relatively easily controllable with relatively low cost components and hence are frequently used to control knocking. Particularly, there have been known many anti-knocking devices using ignition timing control.
The conventional anti-knocking device using ignition timing control utilizes a feedback control system in which, when knocking occurs, the ignition timing is delayed from a predetermined reference angle by a constant angle or an angle corresponding to the degree of the knocking. When knocking ceases, the delay angle is reduced at a high rate, for instance, 0.5.degree. /sec., so that the ignition timing is set near the knocking limit at all times.
In the above-mentioned ignition timing control system, it is necessary to set the reference ignition timing at a well-advanced angle. Therefore, the ignition timing at the commencement of knocking control frequently exceeds the knocking limit, causing a large amount of knocking to appear.
Further, since both small and large ignition timing correction ranges which require knocking restriction are controlled according to the detected knocking signal (feedback signal), a wide dynamic range of the system is necessary; otherwise it is very difficult to perform exact control over the entire operating range of the engine.
In addition to the defects of the conventional anti-knocking device mentioned above, when the operating condition of the engine varies, there is a considerable delay in the feedback signal to reflect such changes. That is, the response to variations of operating conditions is poor.
Other factors such as intake air temperature and intake air humidity, etc., which depend upon changes in environmental conditions, change very slowly. Therefore, the knocking conditions vary over only long periods. In other words, the degree of knocking which occurs in relatively short time periods for like operating conditions of the engine is the same and there is no difference in the frequency and intensity thereof between knocking occurrences. That is, the control amount required to restrict knocking for like operating conditions is substantially the same over short time periods. Therefore, the control value stored in a memory need not be changed over short periods. For the factors which change only slowly, it is possible to correct the control value gradually.